An OPAMP is generally utilized in a feedback circuit in order to amplify an input voltage to a desired output voltage. Generally, the OPAMP consists of two input terminals, (i) a positive input terminal (i.e., non-inverting) and (ii) a negative input terminal (i.e., inverting), and an output terminal. Further, in the context of the feedback circuit, a portion of the output is fed back to the inverting terminal to establish a fixed closed-loop gain for the feedback circuit, G0. The feedback gain G0 is the ratio of the voltage across the feedback circuit element, Vo, to the voltage across the input circuit element, Vin During operation of the feedback circuit, the OPAMP's DC open-loop gain A amplifies the potential difference between the negative and positive inputs of the OPAMP. The open-loop DC gain A of the amplifier will continue to amplify the potential difference between the negative and positive input terminals of the OPAMP until the potential difference is zero. As long as the input and output stay in the operational range of the OPAMP, the output of the OPAMP will be the input voltage multiplied by the closed-loop gain set by the feedback, G0.
However, OPAMPs do not have an infinite DC open-loop gain in real world use. As such, a finite DC open-loop gain A limits the feedback circuit from attaining the ideal feedback gain G0 (i.e., limiting an input voltage from achieving an ideal output voltage). Further, the limited gain A can also introduce error in signal transfer functions, which further limits the performance of the OPAMP. In addition, OPAMPs also have a very narrow output swing range. Therefore, if the output swings beyond the narrow range, the DC open-loop gain of the amplifier A will decrease, which causes the closed-loop gain G0 to decrease as well.
There is thus a need to enhance the DC gain of an OPAMP for circuits with low power consumption.